Manufacturers have developed uncooled IR devices to meet more stringent demands for low weight, compact size, and reduced cost. Uncooled detectors refers to detectors that are not cryogenically cooled, preferably operable within the temperature range of 300 K +/−75 K. There are increasing opportunities to incorporate these uncooled IR detectors into consumer products and electronics, such as automobiles, security devices, medical imaging and the like. Uncooled IR detectors comprise several major components, typically a radiation sensor such as a focal plane array (FPA) that senses incident radiation, a window through which incident radiation passes to the FPA, one or more thermoelectric (TE) cooling elements that remove heat generated by the FPA and incident radiation, a base and sidewalls that, along with the window, define a vacuum chamber that isolates the FPA from the external environment, and a getter that adsorbs or absorbs molecules within the vacuum chamber to prevent package heat transfer to the FPA.
Manufacturing both cooled and uncooled IR detectors remains expensive due to several factors, primarily a multi-step serial process for decontaminating and sealing the detector vacuum chamber. The FPA, typically a heat sensitive resistor, is highly sensitive and responsive to even minute amounts of environmental contamination. Packages are therefore designed to maintain the FPA at very low pressure, typically less than about 50 mTorr, throughout the useful life of the detector. Traditionally, the vacuum chamber was defined by a metal housing made from several components that were sealed using laser or e-beam welders. Metal-body detectors typically include a pinch-off tube extending outside the package that is crimped or otherwise sealed after final evacuation of the vacuum chamber. Ceramic-body detectors now use a solder re-flow process in several steps to seal the detector, leaving only a seal port penetrating into the vacuum chamber once all other components are assembled and sealed. The detector is evacuated by attaching a vacuum pump to the pinch-off tube, or by placing the entire detector into a vacuum chamber. Due to the strict operating requirments imposed by the FPA, proper evacuation of the vacuum chamber often requires hours or days of cycling low pressure and high temperature. Once evacuation is complete, the pinch-off tube or the seal port is sealed.
While the costly traditional metal housing components are being superceded by ceramic housings in more recent designs, final sealing of both metal and ceramic detectors remains a time consuming serial process that raises fabrication costs. The use of solder traditionally adds several steps to the fabrication process due to at least two countervailing factors: difficulty in forming a hermetic soldered seal absent flux, and high probability that solder flux would contaminate the vacuum chamber. Flux is used to improve hermeticity, but it may cause bubbles or voids to form within the soldered seal. Such bubbles may rupture or expand, and either off-gas into the vacuum chamber and contaminate the FPA environment or create pathways that compromise the hermeticity of the vacuum chamber. These potential problems require numerous steps to ensure proper preparation and metallization of surfaces. One fabrication technique for ceramic detectors is to solder the window to a window housing. Since this step may be performed away from the FPA, flux is used to improve hermeticity. Such a soldered window/window housing assembly requires an additional cleaning step to prevent contamination of the FPA during its attachment to the remainder of the detector. When the window/window housing is soldered to the remainder of the detector, only a relatively small seal port remains to evacuate the vacuum chamber of the detector, necessitating long periods within a low pressure processing chamber or attached to a vacuum pump.
FPA sensitivity to environmental contaminants appears to be inseparable from its desirable high field sensitivity, so a low-pressure vacuum chamber continues to be required. What is needed in the art then is a radiation detector package that allows more efficient production methods, especially a detector package that supports lighter and more compact designs. It is an object of this invention to provide such a detector package, as well as a more efficient method for making and finally sealing such a detector package. The advantages of this invention are best realized with uncooled ceramic detectors, but the invention applies also to cryogenically cooled detectors and/or metal-bodied detectors. The description focuses on uncooled ceramic detectors but the claims are not limited to such unless made explicit therein.